1. Field of the Invention
The present invention generally relates to transfers of data between data origination stations and data reception stations through a network such as a multistage interconnect network and more particularly relates to transfers of data which may utilize a fiber optic transmission medium.
2. Description of the Prior Art
It has been known for some time to transfer digital data messages between a data origination or sending station and any one of a plurality of message receiving terminals through a message routing device. Those of skill in the art will be familiar with a number of systems which use electrical modes of data transfer. U.S. Pat. Nos. 4,975,906 and 5,144,622, issued to Takiyasu et al. discuss a local area network (LAN) approach. Somewhat more recently, optical media have been employed for the transmission of digital information.
U.S. Pat. No. 3,710,348, issued to Craft, discusses the design and use of standardized interconnect modules. Each of the modules provides circuitry for the conversion of signals to and from external transmission lines and to and from internal logic levels. The modules utilize internal storage arrays for buffering of data and provide circuitry for handling control signals which are transmitted separately from the data signals. Additional circuits are used to provide parity generation and checking features.
The major problems associated with the Craft technique result in relatively slow communication between the sender and receiver even though the standardized interface may yield some system level advantages. U.S. Pat. No. 5,168,572, issued to Perkins, gives the promise of greater speed by employing a technique suitable for use with optical media. The buffering feature is eliminated with the general purpose switching elements providing optical paths for multiple levels of switching. However, separate paths are required for control of the switching elements. Similarly, U.S. Pat. No. 4,731,878, issued to Vaidya teaches the need for separate electrical control circuitry to route optical data streams.
An alternative approach is shown in U.S. Pat. No. 5,175,777, issued to Boettle. With this technique, the data signals are transmitted over shared pathways using wavelength division multiplexing. However, separate signal paths are required for control signals with the implication that these paths are electrical in nature, which is similar to the Vaidya approach. The control and data information are packed into the same packets in the electrical system of U.S. Pat. No. 4,771,419, issued to Graves et al. Unfortunately, by packing the control and data information together, the entire message must be buffered within each of the switch elements to permit the switch element to unpack the routing information. This introduces significant delays into the transmission process and necessitates substantially more hardware to implement. U.S. Pat. No. 4,701,913, issued to Nelson, similarly requires buffering of the message.